The present invention relates to the field of electropolishing and, more specifically, to the electropolishing process carried out with an externally applied uniform magnetic field to alter the properties of the electropolished surfaces. This inventive process, magnetoelectropolishing, is carried out using an electropolishing bath composed of a processing tank, a dc power supply, electrodes and connecting wiring, and a controller. The material for electropolishing is selected, uniform magnetic fields are created or formed about the position to be taken by the selected material in the processing tank by using either permanent magnets or electromagnets, and the control parameters are selected for the electropolishing process, i.e., length of time, voltage level, solution temperature. The electropolishing process parameters are met and the time period is completed before the externally applied magnetic field is removed.
The effects of applying an external magnetic field on an electrochemical reaction can be divided into three categories: electron transfer; mass transfer (Lorenz Force]; and, morphology and chemistry of the treated material surface subsequent to dissolution. Electropolishing, a controlled anodic dissolution, is one example of electrolysis. To establish optimum conditions for electropolishing a particular metal, metal alloy, etc., a voltage vs. current curve is plotted and plateau current densities are established. The current densities plateau mainly exists just below the oxygen evolution regime. However, for many metals, metal alloys, etc., the best electropolishing results may be obtained beyond this plateau under oxygen evolution conditions. The best example is a most often industrially used process for electropolishing stainless steels, which are carried out under an oxygen evolution regime.
Electron transfers in electrochemical reactions occur naturally, i.e. corrosion process, or can be induced artificially. Electropolishing by controlled anodic dissolution is an example of the latter. The electron transfer between the electropolished material and the electrolyte solution must occur for the process to work. To obtain the required conditions the potential differences need to be established between anodes and cathodes, which in almost all cases of electropolishing processes is done by applying direct current.
The best way to describe the electron transfer process between an electrolyte and a solid electrode is the energy level model. In metals, from the electrochemist approach, there exists an electrochemical potential of electrons in a metal electrode, i.e. the Fermi level. In an electrolyte three energy levels exist: EOX, ERED and EREDOX. The characteristic of any solid depends on the extent to which the electron orbitals in the highest band are filled. The extent to which the highest orbitals are filled is called the Fermi level. In metals, the highest band of electron orbitals is only partially filled with electrons and these electrons can jump from one state to another with only an infinitesimal change in energy. This characteristic makes metals good electrical and thermal conductors.
In the case of electrolysis processes, when the applied electrical potential begins a redox reaction with the cathode lying along a central vertical axis, the work piece anode surrounding the cathode and the magnetic field surrounding the electrolysis cell, the external magnetic field alters the process most probably by interfering with the electron structure (Fermi level), resulting in the modification of the polarization of the free surface electrons. Further, no one can exclude the possibility of a proton transfer reaction influenced by the magnetic field that can be important both in the presence and absence of electron transfer processes.